The present invention relates to a heat developing device for use with an image recorder of the type in which an image is exposed to, and thermally developed on, a thermally developable sensitive material and the developed image on the sensitive material is transferred to an image-receiving material by overlapping both of the materials on each other.
An image recording method using a specific thermally sensitive material is disclosed in the specification of Japanese Patent Application No. 60-121284 filed by the present applicant. The material comprises a carrier or base coated with a thermally sensitive composition consisting of at least a sensitive silver halide, reducing agent, polymeric compound and colored image-forming substance with at least the polymeric compound and colored image-forming substance being sealed in the same microcapsules. According to this image recording method, a latent image is formed on the sensitive material and then thermally developed, and the polymeric compound lying at a portion where the latent image is present is polymerized to generate a high polymer compound thereby hardening the microcapsules. Then the sensitive material is overlapped with an image-receiving material having a layer capable of allowing the colored image-forming substance to be transferred to the sensitive material, and pressure is applied on the overlapped materials so that the microcapsules at a portion where the latent image is absent are partly broken to cause the colored image-forming substance to be transferred to the image-receiving material to form an image thereon.
A heat developing device for use with an image recorder employed in the above image recording method is shown in FIG. 3. As shown, the heat developing device 401 heats a sensitive material S rolled around a cylindrical heating drum 402. In order to thermally develop the entire surface of the sensitive material S simultaneously, it is necessary for the heating drum 402 to have a circumference larger than the length of the sensitive material S.
Accordingly, where the length of one sheet of the sensitive material S in its feeding direction is large and the area occupied by an image is large, the requirement that the heating drum 402 have a diameter large enough to match the length of the sensitive material S means that the image recorder will inevitably be very large.
In order to solve the above-described problems, it is an object of the present invention to provide a heat developing device of the structure which enables its image recorder to be small in size.